It's Us Against the World
by Wildatheart843
Summary: After an unfortunate accident on a new planet, Keith and Lance find themselves caught in a large web of lies and secrets. I mean, would you tell your teammates that you somehow turn half fish when you touch water? Didn't think so. merman!Lance merman!Keith sort of an H2O/Mako Mermaids Crossover
1. Chapter 1

_So, it has been for-ever since I've posted on this site. I've been so busy between working during the summer, and then school starting, along with some other mental things I've been going through. With everything going on, I just wanted to destress and I thought, why not writing? So, this was poured out all in like 2 hours…_

 _I've been really into the Voltron fandom lately, and I just finished watching the 4_ _th_ _season of Mako Mermaids, so this came about. I'm a sucker for mermaid!Lance ^_^ I'm not too sure if this is any good, but reading other fics about mermaid!Paladins, I thought I'd try my hand at it!_

 _Let me know what you think and If I should continue!_

 _(And sorry if any characters seem OOC, I tried ^_^)_

The Vanderians of planet Vand were a peaceful species, and planning to stop by that planet to form an alliance and add to the coalition was a no brainer for team Voltron. It was decided that Shiro, and Allura would go meet with the council, while Pidge, Hunk and Coran stayed on the ship serving as support. Keith and Lance were given the task of exploring an island just off the coast of the mainland to see if they could gather any provisions to provide something more appetizing than food goo.

The red and blue paladins had been walking forever in what seemed to be circles, the sun already setting and the moon starting to rise, when a clearing up ahead complete with a little river and waterfall made an appearance. Lance smiled and turned to Keith, gesturing towards the clearing, jogging up to it.

"Let's go this way, see what we can fi-IIIND!" Lance's sentence trailed off into a loud yell as he seemed to disappear from sight, his helmet flying out of his grip as he fell. Keith ran up to see what happened, only to meet the same fate as Lance and tumbling down a hole in the dark. The two paladins slide down a tunnel, wide eyed and shouting, until they finally met the ground. Lance fell through first and moved to stand up, only to fall back down as Keith slammed into his back. The two lay on the rough ground in a pile of limbs, groaning in pain at the unexpected tumble.

"Ugh, would you get off! You're heavier then you look." Lance grunted out. Keith rolled his eyes and pushed off the complaining teen. Holding out a hand to help Lance up, they both turned and froze at the sight before them. Sitting before them was a large blue pool of _glowing_ water.

"Is the water… glowing? Or did I fall harder than I thought…?" Lance rubbed his eyes, seeing if the sight would change, squinting in confusion when it didn't.

"Um, yup. It's ah… it's glowing…" Keith summarized. While lance was busy looking at the pool of water, Keith decided to take in their surroundings to find a way out. He looked up in the tunnel they fell from, groaning in annoyance when he realized that a) it was way to steep to climb out, and b) the moon was now high in the sky, probably almost midnight in Earth time.

"The tunnel's too steep to climb out, so unless there's another exit, we're stuck here." Lance turned to look at Keith with a sigh, then continued analyzing the water. He narrowed his eyes as he noticed a slight push in the current, and his eyes widening at the realization of there being an exit after all.

"Hey Keith? Yeah I think there's an exit… but it's down there." Lance called out, pointing down at the pool. Keith groaned and made his way back to the Cuban teen. "Oh come on, its not that big a deal."

"Not a big- Lance! We dropped our helmets up there! How are we going to hold our breath for that long?" Lance's response was to jump into the pool. "Lance!" The blue paladin resurfaced and waved a hand at Keith.

"Relax. I'm just going to swim out and see how far it is. I'll be back in a bit." Before Keith could say anything, Lance was already diving down and swimming through the exit.

Keith waited for longer than he felt necessary, but eventually Lance resurfaced. Keith scrambled over to the edge to see if his team mate was alright. "It's not too far out. If you can hold your breath for at least thirty seconds, depending on how fast you swim, it should be fine." Keith nodded, then grimaced slightly as Lance looked at him expectantly, waiting for the pale teen to get in. "What are you waiting for? Jump in!" Keith bit his lip and sighed.

"Um, I may not be the, uh, best… swimmer?" Lance's eyes widened a fraction before narrowing.

"Keith. We've been in space for almost a year. How has this not come up at all? You've never indicated you couldn't swim!"

"I'm the guardian spirit of fire! It's not really a necessary skill for me to know!" Lance sighed and held out a hand.

"Alright, well we need to get out of here, so just hold onto me and I'll swim us out." Keith shuffled a bit, then sighed. If he didn't trust Lance, then there was no way they'd be getting out of this mess. He took a deep breath and slid into the water, quickly wrapping his arms around Lance's neck when he felt his feet leave solid ground. Lance held onto him tight around the waist. "Ready?" Keith nodded, and the two took a deep breath simultaneously, ready to dive down.

Just as they were about to dive, a bright light shone over them in the pool, the two squinting up to see the moon through the opening of the cavern. They shared a confused look, then gasped as the water around them started bubbling. Keith tightened his hold on Lance, looking around them at the water.

"Lance? W-what's going on?" Lance grimaced at how Keith's voice shook, having never heard the red paladin sound that worried, or dare he say, scared. Lance bit his lip and shook his head at Keith, the two just watching as the weird phenomenon took place.

Eventually the moon passed over, and the water settled. The two teens let out sighs of relief, looking around to see if anything had changed.

"Let's… let's get out of here… this place is starting to give me the creeps." Keith nodded in agreement, and taking a deep breath, the two dove under the water and left behind the mysterious pool.

…

It was the next morning that proved that their little adventure in that pool was more serious than they originally thought.

Lance woke up with a stretch and then made his way to the bathroom in his room, getting ready to do his daily skin care routine. Wetting his face to get started, Lance's brow creased as he felt a weird sensation go through his legs, only to yelp as he suddenly fell to the floor. Lance blinked a couple times, then moved to stand up, only to realize he couldn't. He looked down and barely hid a scream when he saw not his legs, but a _blue scaly tail_ in place. Lance started panicking then, pulling towels off the rack and trying to cover himself up when he heard footsteps outside the door.

"Lance? Breakfast is soon. Are you coming?" Hunk's voice was muffled slightly by the door as he called out to his friend. Lance looked down at his predicament and took in a shaky breath, continuing to try and cover up in case Hunk decided to barge in.

"Um, yeah-yes I-I'm coming. Be right there!" Hearing Hunk's footsteps fade away, Lance groaned and dropped his head back onto the floor. What the heck was going on! Since when did he have a tail?! How was he going to-

Lance's thoughts were cut off when that weird sensation came back, and he looked down to see his tail (his tail!?) slowly turn back into his pajama covered legs. Lance took a deep breath and shakily rose to his feet, foregoing his morning routine and sending a wary look at the sink as he left the room, making his way next door.

He needed to find Keith.

…

Meanwhile, Keith had a slight problem of his own. The red paladin looked down with wide, terrified eyes as a shimmering red tail was resting where his legs once were. One minute he was washing his hands, the next he was on the ground, staring at what looked to be a _mermaid_ tail attached to his torso. _Merman tail_ , his mind supplied him. _Oh yeah, like that's going to help anything_.

The sudden sound of someone banging on his bathroom door in rapid succession pulled him from his thoughts as his gaze snapped to the door.

"Keith! Keith ae you in there? This is an emergency!" Lance. That was Lance's voice. No way was he letting Lance see him like this. He kept silent, hoping the blue paladin would leave, his eyes flicking wildly around the room for any solution. He heard Lance sigh, but instead of hearing footsteps fading away, the door clicked, and was suddenly being pushed open.

"No, no! Don't come-" Indigo and blue eyes met, and both gazed down at the large protrusion attached to Keith's body. Lance looked with wide eyes.

"You too…" Keith squinted. What did that mean?

"Look, I-uh, I can e-explain…" Lance ignored Keith's statement, instead stepping around him and grabbing some towels off the rack. "Um, what are you doing? Why are you not freaking out?" Continuing to ignore the pale teen, Lance started rubbing the towels along his tail, scrubbing until Keith felt a tingly feeling, and his tail morphed back into his legs. Keith looked down with eyes the size of dinner plates, grabbing his legs as if he couldn't believe what had happened. "Wha…" Lance gave him a somber look and rested a hand on his shoulder.

"We need to talk."

…

Lance and Keith were both sitting on the edge of the latter's bed, close enough that their knees were touching. Keith was staring at his hands clasped in his lap, while Lance looked around, eyes searching for answers he couldn't find.

"So… what now?" Keith asked hesitantly. He looked up to see Lance watching him with a contemplative look, bottom lip held between his teeth as he thought. Lance sighed and stood up.

"Now? We have to keep this a secret. From _everyone_." Keith's eyes widened as he stood up, standing in front of Lance, where he only just now noticed the blue paladin's taller stature compared to his. Keith looked up confused.

"Keep this a secret? Lance, we can't hide this from them! Voltron is only able to be formed because of a strong bond between the paladins. Secrets will just get in the way of it and we won't be able to form Voltron." Lance rolled his eyes and crossed his arms.

"I get the whole 'team bonding-form Voltron' thing, I really do. But how do you suppose we go about telling them that we are now some crazy mer-people who turn half fish if we touch water? I don't know about you, but in my head, it ends horribly."

"Well we can't just lie to them all the time. And when they do find out, which they definitely will, they'll be even more upset that we kept this from them! We're in space, Lance. Hiding something like this just isn't going to work."

"I know chances of it lasting are slim, but we don't really have a choice. Say we do tell them, and the Galra end up getting a hold of one of them, and they end up blurting it out loud. The Galra would be able to use it as a weakness and we would be in even more danger."

Keith and Lance both had similar looks of anger, annoyance, confusion, and… fear. What if the Galra really did get word about this? Who would have thought that water would be almost half of Voltron's undoing? Keith sighed and pulled his arms up to wrap around himself, making him look even smaller than usual. Lance frowned and pulled the red paladin into a tight embrace.

"We'll get through this. We just have to stick together." Releasing his hold, Lance held out a fist to Keith, smiling lightly. Keith laughed and bumped his fist against Lance's.

"Together."

…

Lance groaned and covered his face with his hands, pulling them down as he waited as Keith dried him off, the floor in the cryo-chamber freezing on his bare back.

"I swear if I have to run off _one more time_ because of Pidge spilling water on me I'm going to scream." Keith just shook his head and chuckled, squeezing his hand a little tighter to try and hurry the drying process.

Over the past few months, Keith and Lance had gotten really close, much to the surprise and suspicion of the other paladins. Due to their, _unique_ circumstance, they had spent a lot of time together, whether that's trying to find ways of avoiding water without the others obviously noticing, or discovering and practising their new-found powers together.

After an unfortunate battle that left Keith with a large gash on his wrist, Lance had taken to cleaning it and stitching it up to prevent any possibility of water coming in contact with the red paladin. He had been cleaning out the wound when Keith's hand had scrunched up in pain, causing the sheets next to his hand to promptly burst into flames. The two had jumped away, Lance beating the flames out, while Keith had stared at his hand in confusion. After the fire was out, and he had been patched up, Lance filled a glass with water, watching as Keith scrunched up his uninjured hand, only to see the water steam and bubble, eventually evaporating.

For Lance, they had been visiting another planet when one of the civilians had tripped, the glass of water in their hand flying in the air, towards Lance. The blue paladin reacting on instinct had thrown his hands up in front of his face. He had been confused when the water hadn't hit him, and when he looked up, a ball of water was floating in front of his hand. Lance had panicked and dropped his hand, letting the now formless water fall to the ground as he ran off to find Keith, leaving a stupefied villager in his wake.

What led them to their current problem was that a diplomatic meeting for the members of the coalition was being held in the castle, and not even ten minutes into the meeting, Pidge had bumped her glass, spilling its contents all over Lance. Lance had jumped up, sending a frantic look at Keith, and then had promptly leapt onto the table, ran across and jumped down, then sprinted out of the room. Keith had stood up right as Lance had left, throwing out a rushed excuse before chasing after the Cuban teen.

And now, here they were, sitting on the floor in the cryo-chamber as Keith worked at getting Lance back onto his feet - literally.

"Are you almost done? It's freezing in here!" Keith rolled his eyes and tightened his hand into a fist.

"I'm going as fast as I can Lance. But can I just say that your exit from that diplomatic meeting was nothing short of spectacular." Lance gaped as Keith chuckled.

"Did you- you just made a joke! Put this in the history books! Keith Kogane made a joke!" They were both full on laughing, Keith trying to keep his focus on de-tailing Lance. "But seriously, I was just trying to get out of there quickly."

"By jumping on the table?" They chuckled loudly at that. "Alright, now can it so I can focus. This isn't as easy as it looks." Lance laughed with a nod and sat still, waiting to change back. They both jumped when the sound of knocking came from the doors to the cryo-chamber. Lance looked at Keith.

"You locked the door, right?" He hissed frantically. Keith's eyes widened as he shook is head.

"Lance? Keith? Are you guys okay?" The two shared a terrified glance. Shiro. If he saw this then they would have some major explaining to do. Then everything happened at once.

The ever-telling sound of hydraulics moving, the door opening slowly, and Keith and Lance threw their hands up, palms facing the door, shouting, "No!".

The two paladins stared at the now frozen door, open just a crack, in slight horror, looking at their hands in surprise, then smiling at having discovered a new-found ability.

"Guys? What's wrong?" Oh right, Shiro.

Keith finished drying Lance off, the blue paladin pushing himself to his feet as the red paladin moved to unfreeze the door, both calling out reassurances to their leader. When the door was unfrozen and slid open, the sheepish paladins looked up at Shiro, who held a suspicious gaze on them. Finally deciding he wasn't getting anything out of them, all three headed back to the dinning hall, where Lance and Keith both distributed apologies, and then the meeting finally got underway.

…

"Hunk! On your six!"

"Thanks Lance!"

"Lance, watch your back!"

"Got it!"

It was another routine infiltration mission on one of the Galra outposts that the paladins of Voltron found themselves thrown into. Their current mission was to try and get to the main control room and turn off the power so the could hack into the prisoner files and get the captured prisoners to safety. Shiro had gone to find the prisoners with Pidge, while Hunk, Keith and Lance had stayed in the hall just outside of the control room, fighting the droids as the came while trying to get the door open.

"Ugh! It won't budge!" Keith shouted over the sound of blasters shooting, Lance and Hunk covering him as he tried to hack into the software with directions from Pidge sounding in his ear. Lance twisted slightly and smirked at Keith.

"Ah, come on Keith! Don't let that fiery side flame up again. Stay calm!" Keith groaned and tossed a hand up, moving to cover his face with it in exasperation, but freezing when he sees Lance's eyes go wide and dart around.

"Lance?" Keith questioned.

"Dude! Where'd you-" Keith had moved his hand down, watching as Lance's eyes found his. Lance smirked than turned back to the battle. "I am so trying that when we get back to the castle!"

"Try wha-"

"Guys! Focus!"

Pidge's voice rang through the coms, shocking Keith out of his confusion as he turned back to the panel. Half listening to Pidge, Keith looked down at his hand and shrugged. What's the worst that could happen?

He raised his hand, scrunching his fingers and smirking as steam rose from the panel. The panel eventually fried, the door opening with a hiss from the hydraulics and Keith laughed, turning back to Lance and Hunk.

"Got it."

…

That night Lance had pulled Keith into his room, demanding he teach him his 'disappearing act'.

…

 _And that's a wrap! Once again, let me know what you think! Also, Vand is Danish for Water… so creative amiright ^_^_

 _PS: If you follow any of my HTTYD WIP, feel free to send me ideas because I have had writers block for those for I don't know how long… Feel free to PM me or just write a review!_

 _3_


	2. Chapter 2

_Whoa. I got a way better response to this than I thought I would. Thank you everyone who reviewed/followed/favorited! It means the world to me!_

 _I decided to continue with this fic. You guys are very encouraging every time I get an email saying a new person has followed/favorited! I also want to see where this is going to go. I honestly don't have an outline for this, (which I probs should) so if you guys have any suggestions on where to take this, or what you want to see happen, feel free to let me know :)_

"Uggggghhhhh."

Keith glanced up from his position on his bed where he was polishing his knife, narrowing his eyes in annoyance as he looked at Lance. The blue paladin was sprawled out on his back, feet resting on top of the bed, a water ball suspended in the air where he held it. Keith snorted quietly and rolled his eyes, focusing on his knife once again.

"What is it this time Lance?" Lance's dramatic sigh was enough for Keith, who had to listen to his comrade's groaning for over half an hour. The red paladin set his knife down on the bed and slid onto the floor, mimicking Lance's position and raising a hand to play with the water in the air. "Why are you all mopey?"

"Do you know what the worst part about having a tail in space is?" Keith shrugged as he started to evaporate the water, causing Lance to elbow him in playful annoyance. "We can't even go swimming. Or go in water, where we technically belong as part merman." The two raised their hands, using their co-freezing ability to turn the water ball into ice.

"Well, the castle has a pool… we'd have to figure out how it actually works, but then we could swim in that."

"But does the pool room have a lock? I don't know about you, but I do not want someone walking in on me when I'm half fish. And then there's the cameras…" The two shot up simultaneously, the forgotten frozen water ball shattering as it made contact with the floor. The boys scrambled away from the solid water, then both stared at each other in panic.

"The cameras!"

…

In the Castle control room, Allura, Coran and Shiro sat talking as the went through the ship's surveillance footage.

"Even though Ulaz making it onto the ship didn't turn out too terribly, we need to figure out how he got in so we can prevent that from possibly happening in the future." The Princess stated. Shiro nodded from where he was standing behind Coran, the royal adviser having placed himself in front of the footage screen as he looked through the videos.

"How he could have even gotten in without setting off the alarms immediately is quite concerning, but don't worry Princess! We will have this sorted out in just a few ticks!" Allura laughed and stepped up to the unoccupied side by the screens. Searching through the footage from that day, Shiro smiled slightly as he watched the teens on board go about their free day, Pidge in Green's Hanger on her laptop set atop her Lion's paw, Hunk baking in the kitchen, Lance laying on the floor in… Keith's room?

"Wait, wait! Stop!" Shiro quickly gestured to a screen that showed Lance laying on the floor in what was now definitely confirmed as Keith's room as said paladin moved to sit next to him. Shiro took a closer look at the screen, squinting in confusion as he looked slightly above Lance's outstretched hand, then watching as Keith's hand raised up as well. "Is that…" Allura and Coran moved closer as well. "…water?" The three watched as the red and blue paladins talked, but mostly paid attention to the _water ball floating in midair and changing forms_.

"What the quiznak is going on here?" Coran twirled his mustache as he watched the video footage of what was happening right at that moment from the other side of the castle. They all jumped slightly as the two teens onscreen jumped up, the ice shattering onto the ground. Keith and Lance both looked panicked as they said something and then ran out of the room.

"Coran… figure out where they are headed." Allura said sternly, Coran nodded, doing as told and switched to the corridor footage. The three watched as they rushed down the halls, their mouths moving a mile a minute.

"Hmm, looks like they are headed… here?" The sound of rushed footsteps outside the door to the control room caused everyone to freeze. Shiro, shaking out of his stupor first, grabbed the two Alteans' arms and pulled them behind the control panel just as the red and blue paladins entered the room. Siro placed a finger over his mouth, a silent message to both Alteans to stay quiet.

"Do you know how to find it? Please tell me you know how to find it. If anyone sees that we are _toast_." The three hiding heard shuffling and slight cursing as red booted feet stepped up to the panel.

"I-I don't know! Shiro always did this stuff with Coran! I was never there." Tapping could be heard, before silence. "U-um Lance? The footage is… already up…"

"What!? Crap Keith, this is bad! Delete it! Delete it!"

"Would you be quiet for two seconds so I can figure out how to do this?" After a little shuffling amid the silence that flooded the room, Lance voice could be heard as a horrified whisper.

"Do you think anyone saw us with the water?" Shiro, deciding now was as good a time as any, nodded to Allura and Coran. The three all stood up in sync, turning to see two frozen teens.

"We saw."

Keith and Lance stared at their leader with wide, horrified eyes at having been caught in the act. If Shiro really thought about it, they looked like two kids who were just caught with their hands in the cookie jar. Shiro narrowed his eyes slightly, then walked around the panel, grabbing one arm of each paladin and dragging the two out of the room. "We need to have a talk." The red and blue paladins shared a terrified glance as they were dragged off by their leader.

…

The right side of Voltron sat in silence as they waited for Shiro to process their- unique -story as he paced back and forth in the common room.

"So, let me get this straight. You two, somehow managed to fall into this weird pool of water when we were visiting the Vanderians, which led to you guys now having magical powers and a mermaid tail when you touch water."

"Well, _merman tail_ , if you want to be technical." Shiro shot Lance a glare, causing the Cuban teen to shrink in his seat. Shiro then turned his gaze to Keith, who had kept his head down during the entire confrontation.

"Keith? Do you have anything to add?" Keith's gaze flicked from Shiro, to Lance, and then back to his clasped hands in his lap. He shook his head, biting his bottom lip. Shiro sighed. "Keith… you know I'm not mad at you guys, right?" Both paladin's heads snapped up looking at their leader with wide eyes.

"You… you're not?" Lance squinted in confusion. Keith just kept looking at Shiro in disbelief.

"No. Look, I understand why you didn't tell me-tell us, but I just wish you would've come to us and then we wouldn't- Keith?" Shiro jumped as the red paladin rammed into him, causing him to lose his balance for a moment. He looked down to see Keith holding onto him tightly, sniffing slightly as he squeezed their leader. "Keith, what's wrong?"

"I-I thought you were g-gonna be mad and l-leave me…" Shiro's eyes softened as he wrapped his arms around the distraught teen. He looked up at Lance who shrugged and made an 'I'll tell you later' gesture. Shiro squeezed Keith slightly before putting his hands on his shoulders and pulling him back slightly. The black paladin smiled and ruffled Keith's hair.

"I'm not going anywhere. I'm going to be here to help you guys through this, okay?" Keith nodded and smiled slightly, using his jacket sleeve to dry his wet eyes. "That being said… I do think you should tell Hunk and Pidge considering that they started making bets that you two are secretly dating." Keith jerked back slightly as Lance jumped up from the couch, both wide-eyed in disbelief.

"Dating!?" Shiro laughed slightly as he watched the two flush bright red when their eyes met, both turning away from each other, Keith in stunned silence, and Lance gong on about how improbable that notion was. Sighing, Shiro placed a hand on both their shoulders, pushing them towards the door. They looked up questioningly and Shiro just rolled his eyes fondly.

"We can talk about this whole merman business in the morning, you two need some rest." Lance held up a finger, quickly turning back to Shiro.

"Wait! But what about the foota-"

"Don't worry about it. I'll handle it. Now go get some sleep." Shiro smiled as he watched the two still blushing teens leave the room, the doors hydraulics hissing as it closed behind them.

…

"Do you think we should tell Pidge and Hunk? I mean the others know so why not? Plus, I don't want them getting the wrong idea! I mean us? Dating? That's-" Lance paused in his rambling to take a good look at Keith. The teen had his shoulders hunched slightly, his arms loosely crossed, and his bottom lip in between his teeth. His thumb was rubbing against his pointer finger swiftly as they walked. Lance stopped walking and placed a hand on Keith's shoulder. "Hey… are you okay?" Keith looked up at Lance for a moment, the two staring before he dropped his gaze again.

"Um, yeah. M'fine." Keith mumbled. Lance kept his eyes on Keith, brows furrowed in concern. Before Lance could question him, Keith shrugged out of his grip slightly and headed towards his room. "I'm gonna go get some rest. Night Lance." Keith walked down the hall and was about to turn the corner when Lance called out to him. He looked up to see a reassuring smile on his friend's face.

"Hey. If you need anything or want to talk, I'm here." Keith smiled gently and nodded.

No matter what happens next in this crazy life full of twists and turns, Keith will always have Lance by his side.

 _meladi 1: I know! I was always wondering that like how is that even sanitary? For the purpose of this story let's just say there Is some form of sanitizer that doesn't contain water ^_^ It's space, anything can happen._

 _DriftingGem: I was writing out this chapter and all I could think was 'man these two are literally going to start a betting war on the ship'._

 _It's a bit shorter than last chapter, but work and school has piled up on top of me. I'll try to update soon :)_


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